This invention relates to the use of hot melt pressure-sensitive adhesives which adhere well to the human skin and hair, and are therefore useful for a variety of medical and other products.
Although many adhesive compositions are known, very few of these are completely satisfactory for application to human skin. The requirements for such adhesives are stringent; they must adhere well to human skin during perspiration, when the weather is hot, or in an environment of draining wounds, yet be removable without leaving adhesive residue on the skin's surface. Moreover, adhesion should take effect immediately on application to skin, even in a hot or moist environment, and should release cleanly and with minimal discomfort when voluntarily removed in this environment.
Adhesives applied to sensitive areas of the human body require further special characteristics. Hair covered regions are especially difficult to adhere well to without causing pain upon removal of the adhered article. For such regions, a soft adhesive with minimal viscoelastic loss is required. Hydrogels have been used effectively for such purposes, but have their own disadvantages, including high price, special packaging and release layers to retain the moisture (typically about 40% of the total adhesive), as well as variations in properties during use in response to changes in humidity. Other disadvantages arise from the general necessity of a non-woven support to strengthen the adhesive and hold it in place during cure. Once cured, a water impervious release layer is applied.
To obtain a soft adhesive while maintaining solid-like behavior requires high molecular weight polymers be used. With hydrogels this is obtained by crosslinking or curing after cooling, as is the case with an electron beam curable acrylic described in European Patent Application EP 175562 A2. Further, U.S. Pat. No. 5,262,468 to Chen describes the use of very high molecular weight rubbers to obtain gelatinous thermoplastic compositions, but such compositions generally lack in adhesive grab so that virtually no adhesion to the body is obtained.
It is an object of the present invention to obtain an adhesive with the desirable characteristics of a hydrogel, but without the drawbacks. In particular, a hot melt adhesive has been discovered that requires no subsequent cure, but functions like a hydrogel.